1. Field of the Invention
This invention relates to air-operated diaphram spring brakes of the type employing a push rod actuator and used with air brake systems on vehicles such as trucks. More particularly, the invention relates to a stroke indicator which is integrally marked on the push-rod actuator to visually show when the brake is out of adjustment or when brake system components are not functioning properly.
2. State of the Prior Art
A typical air brake system for a vehicle such as a bus, truck or the like includes separate brake means such as a brake shoe and drum at the vehicle wheels. The brake shoes are actuated in one direction to apply the brakes and in the other direction to release the brakes. The brake means may serve as both service and emergency brakes, and individual brake actuators are located adjacent the wheels for actuation of the brake means.
A typical brake actuator includes a service brake actuator for applying and releasing the brakes in response to delivery and exhaust of compressed air. Often a spring brake actuator is disposed in tandem with the service brake actuator. The spring brake actuator uses the force of a strong compression spring to operate the service brake actuator and apply the brakes when air in a spring chamber is reduced below some predetermined level. Air may be reduced in the spring brake actuator under the control of the operator in the manner of a parking brake, or automatically in emergencies such as a failure of portions of the service brake air system.
The brake actuators typically employ diaphragms that move in response to air pressure and springs. The diaphragms in turn actuate push rods which move the brake means between operative and inoperative positions.
With structures of this general type, it is frequently difficult to determine when the brake linings or pads have become worn to the extent that the brakes need adjustment or replacement. Frequently, the operator or mechanic either had to visually estimate the position of the brake mechanism with brakes applied versus the unapplied position or had to physically measure the stroke of the push rod. Prior solutions for determining such wear have included complex and expensive mechanical and electrical components to measure the amount of stroke through which the push rod moves. Other devices require the addition of discs or pointer brackets to the service brake housing and to the push rod to measure the stroke. Visual indicators include the use of adhesive stickers applied to the push rod. All such devices are subject to wear and can easily be jolted out of adjustment or separated from the brake actuator as a result of excessive vibration, heat, dust, weather and wearing of components during normal use.